An in vitro system to study interactions between bacteria and epithelial cells at the molecular level.

This paper describes an experimental system to study interactions between porcine enterotoxigenic Escherichia coli (ETEC) and porcine intestinal epithelial cells in vitro at the molecular level. Radiolabelled bacteria or bacterial membrane fractions were incubated with brush borders prepared from purified epithelial cells, which were then washed repeatedly. The bacterial components removed by washing or retained by the brush borders were analysed to determine their composition and source. For this it was necessary to develop a minimal medium in which attachment factors of porcine ETEC could be radiolabelled. Furthermore, an improved method for the isolation of porcine intestinal epithelial cells was developed, since other procedures did not yield sufficiently pure preparations. The resulting method was rapid and yielded large quantities of viable epithelial cells, free from crypt cells and contaminating intestinal contents. Finally, we adapted existing procedures to isolate brush borders from these epithelial cells with special emphasis on the removal of nuclear and cytosolic material and on the isolation of morphologically intact brush borders. Using this system, mixtures of bacterial cytoplasmic and outer membranes were incubated with brush borders. Cytoplasmic membranes were easily removed by washing, while the outer membranes were not.